The invention relates to a method and an apparatus for reverse playback of a digital data stream representing video information.
For processing a digital data stream, which is e. g. Video CD MPEG 1 coded, a sequence of a consecutive sector stream will be provided by a Pickup, retrieving these sectors from a disc. For trick mode the MPEG I standard ISO/IEC 11172 xe2x80x9cCoding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/sxe2x80x9d Part 2: Video supports features by an algorithm for fast search and reverse playback.
For fast search, depending on the storage medium, it is known to scan the access points in coded bitstreamsxe2x80x94with the help of an application-specific directory or other knowledge beyond the scope of this part of ISO/IEC 11172xe2x80x94to obtain a fast-forward and fast-reverse playback effect.
Some applications may require the video signal to be played in reverse order. This can be achieved in a decoder by using memory to store entire groups of pictures after they have been decoded before being displayed in reverse order. An encoder can make this feature easier by reducing the length of groups of pictures.
In the Video CD specification, Version 2.0, section VII.3 it is recommended to encode Scan Information User_data_groups. If Scan Information User_data_groups are present, then they must be included as user_data in the picture layer of all Intra pictures. Scan Information data contains forward and backward pointers to Sectors that contain the start of an Intra picture. A file xe2x80x9cSCANDATA.DATxe2x80x9d must then be present on the disc. However, the Scan Information User_data_groups is not often used.
In order to provide backward trick modes in case the Scan Information User_data_groups is not available one typically implementation is known:
1-jump n sectors backwards
2-decode next pictures from new starting point
3-display only I Frames
1-jump again
The digital data stream of an e. g. Video CD MPEG 1 coded is organized in at least Group of Pictures (GOP) and Sectors. GOP starts usually with an Intra picture followed by several Non-Intra pictures. The number of Non-Intra pictures could be fixed or variable. Therefore, since step 2 is just a xe2x80x98show me the I Frames in a certain sequence portionxe2x80x99 it might happen that two Intra pictures will get displayed which are in the wrong order for a backward trick mode.
Displaying preceding I Frames in a step by step manner using a jump back scheme will not be smooth because of not regular sectors per GOP structure.
It is an object of the present invention to disclose a method, which allows stepping backwards displaying each consecutive picture.
According to the invention, this object is achieved by means of the features specified in main claims. Advantageous designs and developments are specified in subclaims.
According to the invention for processing a real backward trick mode the sectors coming from the Pickup are resorted to a reverse order. A parser algorithm is then searching the next Intra picture start and if found will queue only the appropriate Intra picture sectors to a Video Decoder.
In particular the inventive method for reverse playback of a digital data stream representing video information, this information being stored in an Intra picture coded format followed by several Non-Intra coded pictures, the video information being organized in sectors containing a fixed number of bytes, includes the following steps:
jumping back n sectors from the actual scanning position, reading an address information of the n sectors in forward direction,
creating therefrom a sector location list,
resorting the sector location list to a reverse order,
parsing the position of sector stream according to the reversed sector location list in order to find appropriate
position of start codes of the video information,
delivering the digital data stream from this position to a following processing unit.
Since the position of an Intra picture start is now known it is possible to
a) request a new sector stream which will be definitely preceding the current Intra picture and
b) request a new sector stream which will be definitely consecutive to the current Intra picture.
For performing a real backwards parsing a new scheme of start code parsing for detecting overlapped start codes has to be used.
The invention provides a stepwise backwards trick mode which is not common on Video CD players. Also, it provides the display of consecutive Intra pictures in backward trick modes.